Interessant artikel:
http://scialert.net/fulltext/?doi=pjbs. ... 963&org=11
Advances in Leptospira vaccine developments: Advanced tools and techniques like of recombinant DNA technology, reverse genetics, DNA vaccination strategy and others, are being explored employing novel antigens, proteins and genes as potential candidates to get safer, efficient and better vaccines for leptospirosis (Koizumi and Watanabe, 2005; Lutticken et al., 2007; Adler and de la Pena Moctezuma, 2010; Murray et al., 2012). Virulence of Leptospira is attributed to multiple virulence factors which play vital role in pathogenesis. These virulence factors include hemolysins, outer membrane proteins (czcA and its subunit peptides) (Umamaheswari et al., 2012) and lipoproteins and appeared to be a potent candidate for vaccine development. Leptospira cell components like Hsp58, hemolysin SphH, ChpK, FlaA, FlaB, outer membrane proteins OmpL1 (Gebriel et al., 2006; Vedhagiri et al., 2009), omp like proteins Lag42, Loa22, Lk73.5 (Koizumi and Watanabe, 2003a, b; Artiushin et al., 2004) hemolysis-associated protein 1 (Hap1) (Branger et al., 2001); immunoglobulin-like (Lig) protein LigA and LigB (Palaniappan et al., 2006; Silva et al., 2007; Coutinho et al., 2011), Lipoproteins eg. LipL21, LipL32, LipL41, LipL45 (Matsunaga et al., 2002; Cullen et al., 2003; Seixas et al., 2007; Feng et al., 2009; Luo et al., 2009; Vedhagiri et al., 2009; Grassmann et al., 2012; Murray, 2012), lipoprotein-like complex Glycolipoproteins (GLPs) (Diament et al., 2002) are major virulence factors and potential candidates for recombinant vaccine. Among them a pore forming protein ‘Hsp58’ and a factor encoded for genes responsible for cytotoxicity ‘ChpK’ have been targeted as vaccine agents (Picardeau et al., 2003).
Probably, development of recombinant vaccines against the outer membrane proteins (omp) of Leptospira might allow concurrent protection against multiple serovars (Nascimento et al., 2004). Moreover, variation in the expression of omp in different serovar also suggests these omps viz., Lsa21, Lsa66 and rLIC11030 either combined or used in a mixture with novel adjuvant have the potential candidate for vaccine development (Umamaheswari et al., 2012; Atzingen et al., 2012). Studies have proved that recombination of protective antigen genes viz., lipL32, lipL41 and ompL1 and a DNA-protein gives better immune responses than single-component, LipL32, or single DNA or protein immunization against Leptospira (Feng et al., 2009). Thus the recombinant vaccine with these potential candidates provides a window to develop a safe and effective vaccine against human leptospirosis. Although all the trials are in preliminary stages and a long path is to be travelled to get effective and safe recombinant vaccine. In a recent study, conducted to evaluate the immune protective potential of leptospiral recombinant antigens, out of 27 antigens 13 were found to induce protective immune responses in the hamster model and only two recombinant proteins LIC10325 and LIC13059 induced significant protection against mortality (Felix et al., 2011). These results have important implications for advancing the development of a successful recombinant subunit vaccine against leptospirosis.
Being Gram negative bacteria Leptospira also express lipopolysaccharides (LPS) and these could be another potential candidate for the development of good and safer vaccine. Initially LPS was reported to have dose and administration dependent serovar-independent potential with some contrasting findings (Matsuo et al., 2000) keeping it open for further investigation. During this journey identification of LPS fractions and LPS like substances (LSSs) with antigenic potential and capability of protection were also attempted and Leptospira-derived LPS has revealed a promising immune potential. Moreover, cross-protection against multiple serovars due to mutation of LPS is suggested (Srikram et al., 2011). Scientific community is exploring LPS for more than last two decades with diverse results and success of LPS and LPS factor based vaccines but it is still under question (Humphryes et al., 2012).
The concept of “reverse vaccinology” using the desired proteins and characteristics with the help of computer data based are the newer opportunity for the development of bacterial vaccines (Serruto et al., 2004; Murray et al., 2012). The known full genome sequence of Leptospira strains (Nascimento et al., 2004) have been used for the identification of potential antigen (Gamberini et al., 2005). On the basis reverse vaccinology, 226 genes encoding conserved and potentially surface-exposed proteins in the bacterium have been identified as vaccine candidates in the genome of L. interrogans and might also be helpful for diagnosis of leptospirosis (Yang et al., 2006). However, the immune status with these candidates is yet to be established.
Similar to other bacterial diseases scientists are also trying for DNA vaccines against Leptospirosis (Branger et al., 2005), following the concept that these might be produced at low cost and be easily administered with safety (Wang et al., 2004; Meykadeh et al., 2005). However, the trial for Leptospira DNA vaccines are still in early stages and only laboratory trials with limited success are reported with genes encoded for hemolysis-associated protein 1 (Hap1), endoflagellin gene flaB2 (Branger et al., 2005), ompL1 DNA vaccine in hamster (Maneewatch et al., 2007) and lipL21 DNA vaccine in guinea pig (He et al., 2008). The CpG motifs within the flaB2 gene could give the DNA vaccine an additional immunostimulatory property, without the use of adjuvants (Dai et al., 2003). Research has proved that the recombination of antigen genes like lipL32, lipL41 and ompL1 and a DNA-protein may provide better results in comparison to that of single components (Feng et al., 2009). No doubt DNA vaccine in bacterial diseases revealed encouraging results but success for Leptospira vaccine is still questionable due to sero-variations and need more extensive investigations (Wang et al., 2007).
Novel and efficacious vaccines developed for emerging infections like of Leptospira in animals can safeguard animal health and also prevent transmission of zoonotic pathogens to humans. Also vaccination of reservoir hosts provides additional advantages to combat zoonotic diseases having public health implications. Options for changes in the Leptospira components of dog vaccines have been suggested for inclusion of serovars Bratislava and Grippotyphosa in Europe. But continued inclusion of serovars Icterohaemorrhagiae and Canicola, with other serovars, such as Pomona, to be considered in the future only after necessary research to support their inclusion (Ellis, 2010). Emergence of Leptospira serovars in particular countries like after the recent report in Greece regarding the presence of serogroup Pomona and serovar Bratislava, emphasizes a need for considering these serovars to be included in future Leptospira vaccines for dogs (Arent et al., 2012). Recently, Kulpa-Eddy (2012) reported successful development and validation of an in vitro replacement assay (ELISA based) for Leptospira vaccine potency tests.
A better understanding and more insights are required about Leptospira spp. biology, pathogenesis, immune mechanisms, identifying leptospiral immunogens, genetic makeup and molecular genetics, which would altogether have important implications for the future prevention of leptospirosis and pave the development of novel intervention strategies to curb this neglected disease. The recent availability of complete genome sequences for Leptospira spp. is a great success in this direction. Recent proteomic studies applied to leptospirosis, characterizing outer membrane proteins and identifying potential leptospiral immunogens, may lead towards the development of rapid and more accurate diagnostic tests and vaccine and vaccine development (Thongboonkerd, 2008). The published full-length genome sequences of Leptospira strains need to be screened for identifying potent leptospiral vaccine candidates utilizing advances in biotechnological and molecular tools and techniques like that of recombinant DNA technology, genetic tools for their transformation, high-throughput cloning and expression, in-silico analysis, comparative genomic hybridization (CGH) analysis, transcriptional analysis, reverse vaccinology, bioinformatics and others (Yang et al., 2006; Ko et al., 2009). More and more genetic information pertaining to Leptospira need to be exploited and explored to combat the disease.
LIMITATIONS OF VACCINES
Presently available vaccines against leptospirosis are of low efficacy, possess undesirable side-effects, induces only short-term protection, does not provide cross-protection against different pathogenic serovars of Leptospira (Koizumi and Watanabe, 2005; Yang et al., 2006). There is a study of development of auto immune disease such as uveitis due to whole cell Leptospira vaccine. In addition, there can be painful swelling after revaccinations (WHO-ILS, 2003) as reported in Cuba when vaccine against leptospirosis was studied to evaluate efficacy and safety, it was found safe with minor side effects (Martinez et al., 2004). Moreover, vaccines are not always recommended due to lack of effectiveness and also due to adverse events (Levett and Haake, 2012). In addition, vaccines produce only agglutinating antibody to specific serovars thus individual once vaccinated will always produce hindrance in diagnosis as these agglutinating antibodies cannot be differentiated from antibodies produced by natural infections. However, the generation of agglutinating antibodies does not always reflects the protection (Levett, 2003) and developments of antibodies against those serovars which were not included in vaccine, this also further create hindrance in diagnosis (Goldstein et al., 2006). It is further aggravated as most of the presently available leptospirosis vaccines for humans are serovar-specific and require repeated yearly vaccination i.e. yearly boosters (Koizumi and Watanabe, 2005; Levett and Haake, 2012).
Post vaccination renal infection and persistent leptospiruria has been observed in immunized dogs along with transmission to human from asymptomatic immunized dogs due to shedding of leptospires in their urine. Moreover, the development of carrier state in animals is of major concern (Green-McKenzie and Shoff, 2010).
In view of the above limitations, the current major focus in search for an efficacious and safer leptospirosis vaccine is to discover conserved protective antigens eliciting longer-term protection against a wide range of Leptospira, providing cross-protection against different serovars of pathogenic leptospires.
Key points for prevention and control:
• All the precautionary steps should be taken to avoid the exposure of infected excreta of domestic and wild carrier animals
• Proper personal, protective measures like wearing gumboots, goggles and rubber gloves should be used in high risk areas
• Strict hygienic measures should be practiced in farms, kennels and animal sheds to avoid transmission of infection through contaminated feed and water by urine
• Some disinfectants like calcium chloride, sodium hydroxide or sodium hypochlorite can be used
• Isolation of the infected persons or animals from the infected one
• Recovered animals should be kept separated for at least two months
• Measures to control rodents, an important reservoirs
• Pre-exposure antibiotic prophylaxis by doxycyclin can be used in endemic areas
CONCLUSION AND FUTURE PERSPECTIVES
Since vaccines are used in apparently healthy humans as well as animals to make them immune to diseases, so it should be safe enough to be administered. Presently existing two types of Leptospira vaccines, attenuated and inactivated, are being used in animals but still have safety concern. Inactivated vaccines are comparatively safer than attenuated vaccines but the level and duration of immune response is to be compromised. The combination of attenuated and inactivated vaccines are also reported with better immune response, however attempts for the inactivation of virulence factors without compromising immune response might be another option. Still, a long way to go to get a safe, effective, single vaccine to get protection against all the serovars of Leptospira as the selection of type of vaccine is not easy. Recent study on leptospirosis is being focused mainly on identifying leptospiral immunogens and protective antigens to be used for diagnostics and vaccine developments. Use and development of recombinant and DNA vaccines with potent immunogenic moiety and genes encoded for the expression of potent immunogens, respectively show a spark of hope. Regular and continuous epidemiological and environmental surveillance actions are suggested, utilizing advanced diagnostic tools, to know the genetic diversity and emergence of Leptospira serovars/strains, which would be much helpful in designing appropriate prevention and control strategies for this important pathogen affecting animals and in humans. It would also help formulating newer multivalent vaccines with most prevalent leptospires and also developing novel and safer vaccines employing advanced research in the field of vaccinology. However, till then application of presently existing vaccines with different adjuvant and routes could be attempted to enhance the immune response with more safe administration.
. En ik ga nog verder. Ik denk dat ze mogelijk dieren proberen gevaccineerd te krijgen om de mens te beschermen tegen bepaalde vormen van Lepto.
Maar van wat ik allemaal lees, lijkt me het te kloppen dat de baten van het vaccin niet tegen de lasten opwegen zeg maar.
